A fuel-air mixture is burnt in an internal combustion engine by inserting a cylindrical part of an ignition coil into a plug hole provided in the engine, and igniting a spark plug attached to a tip in an axial direction of the cylindrical part.
Moreover, ozone gas etc. due to a high voltage is generated in the plug hole. Therefore, a ventilation passage is formed to the ignition coil in order to ventilate these gases with air outside in the plug hole.
In addition, in the process of the engine that is cooled from the warm state, pressure in the plug hole becomes negative pressure by the gas in the plug hole being cooled.
At this time, if the ignition coil is flooded with water, water might enter into the plug hole from the ventilation passage.
Therefore, formation of the ventilation passage is specially designed to prevent water being flooded by arranging a sealing rubber etc. between the ignition coil and an opening of the plug hole.
For example, an ignition coil (igniter) with a well-planned ventilation passage is disposed in JP 2008-60188.
In this ignition coil, on a side of a head that is disposed outside in the plug hole, a water collecting chamber that collects the water infiltrated from the outside of the head and a ventilation passage that communicates between the water collecting chamber and the plug hole are formed.
Further, the water such as washing water may be surely prevented from infiltrating in the plug hole by collecting the water in the water collecting chamber, and the water collected in the water collecting chamber may be drained easily.
Moreover, in the ignition coil device for the internal combustion engine disclosed in JP 2007-303401, it is disclosed that a space part is formed in an upper part of a connector case, a penetration hole is formed from the space part downwardly, and a penetration opening is communicated with the plug hole by a trench.
However, in JP 2008-60188, when the water flows down along a sidewall portion of the head, the water is likely to infiltrate into a ventilating opening disposed under the water collecting chamber.
Moreover, in JP 2007-303401, the space part is formed by a cover that covers the connector case, and the ventilation of the space part is enabled by a gap formed between the cover and the connector case.
Therefore, differences might be caused in the formation of the gap, and there is a possibility that the water may be infiltrated when the gap is enlarged while enough ventilation becomes impossible when the gap is narrowed.